Despite aggressive therapies surgical resection, radiation, and chemotherapy, Glioblastoma Multiforme (GBM), the most common primary malignant brain tumor, remains uniformly lethal due to recurrence and therapeutic resistance. The inability to adequately treat these tumors may be due in part to a subset of tumor cells, cancer stem cells, that are resistant to many conventional therapies. Cancer stem cells within GBMs are localized to several areas, among them the perivascular compartment, which is a known cancer stem cell microenvironment or niche and has been shown to play a role in therapeutic resistance. Adhesion is a hallmark of the stem cell state and identifying adhesion mechanisms specifically used by CSC to communicate with their microenvironment has is of immediate importance and implications in the design of more effective glioma therapies. We have recently uncovered a CSC-specific adhesion mechanism, junctional adhesion molecule-A (JAM-A), and our preliminary data show that JAM-A can be targeted to attenuate CSC phenotypes but has no major impact on normal neural function. Based on these findings, the hypothesis of this proposal is JAM-A specifically regulates niche interactions in CSC and is a potent anti-GBM target. This hypothesis will be evaluated by: 1) interrogating the regulatory axis of JAM-A to show the molecular mechanism of JAM-A regulation; 2) determining how JAM-A targeting inhibits CSC function but not normal neural cell function; and 3) evaluating how targeting JAM-A in combination with radiation and chemotherapy impacts CSC-driven tumor growth. Experimental studies will utilize human GBM specimens and normal neural progenitor cells to evaluate JAM-A targeting by RNA interference or blocking antibody administration. Function will be assessed using a variety of CSC assays and will include evaluation using an intravital imaging model to study the in vivo communication between CSC and the niche in the context of JAM-A inhibition. The long term objective of this proposal is to develop GBM therapies with increased therapeutic efficacy that target the CSC in combination with conventional therapies, while not compromising normal neural function. These studies outlined in this proposal will uncover the critical role of CSC interaction with the niche via JAM-A and evaluate potential therapies to GBM which disrupt niche related communication. Any findings and therapeutic developments may extend to other tumor types with a cancer stem cell component (i.e. colon, breast).